/*功能:过滤掉特殊字符如",<,>等
* @param  str 要过滤的字符串
* @return st 过滤之后的字符串
*/
function stringfilter(str){
	var st = "";
	if (str.length == 0) return "";
	for (var i=0; i<str.length; i++) {
		  switch (str.substr(i,1)) {
				  case   "\""	:   st   +=   "";	break;
				  case   "<"	:   st   +=   "";	break;
				  case   ">"	:   st   +=   "";	break;
				  default		:   st   +=   str.substr(i,1);  break;
		  }
	}
	return st;
}